1. Field of the Invention
The present invention relates to a pretensioner device which is provided at a webbing retractor which takes up a webbing (belt) for restraining a vehicle occupant in layers on a take-up shaft, the pretensioner device rotating the take-up shaft by a predetermined amount in a webbing take-up direction instantaneously due to a gas generating means operating at the time when a vehicle rapidly decelerates or the like.
2. Description of the Related Art
As can be seen in Japanese Patent Application Laid-Open (JP-A) No. 2004-175279 for example, there are webbing retractors which are provided with a spool (take-up shaft) around which a webbing is taken-up in layers, and a pretensioner device which forcibly rotates the spool in a webbing take-up direction when the vehicle rapidly decelerates.
In this type of pretensioner device, a clutch mechanism is set such that the connection with the spool is cut-off at usual times, and the clutch mechanism connects with the spool only when the vehicle rapidly decelerates. There are various types of this clutch mechanism, but hereinafter, the clutch mechanism disclosed in JP-A No. 2004-175279 will be explained and studied.
In the pretensioner device disclosed in JP-A No. 2004-175279, a torsion bar, which functions as a force limiter, is disposed in a state of being inserted in the axially central portion of a spool. The clutch mechanism, which is structured by a sleeve, a pinion (rotating body), and a clutch plate, is disposed coaxially at one end portion in the axial direction of the torsion bar. The sleeve is formed substantially in the shape of a cylindrical tube, and fits-together with one end portion in the axial direction of the torsion bar so as to be unable to rotate relative thereto. Accordingly, when the spool rotates, the sleeve rotates integrally therewith via the torsion bar.
The inner peripheral surface of the sleeve is subjected to knurling. A plurality of meshing claws, which are formed by cutting and raising at the axially central side of the clutch plate, are disposed in a state of facing the knurled surface. The plurality of meshing claws fit-together with the valley portions of windmill-like engaging teeth formed at a pinion. The pinion meshes-together with a piston having a rack bar. The piston moves due to a gas generating means operating at the time when the vehicle rapidly decelerates. When, due to the movement of the piston, the pinion is rapidly rotated, the plurality of meshing claws of the clutch plate deform and ride up on the mountain portions of the engaging teeth of the pinion, and engage with the knurled surface of the sleeve. In this way, the rotation of the pinion is transmitted to the sleeve via the clutch plate, and the spool is rotated in the webbing take-up direction integrally with the torsion bar and the sleeve.
In the pretensioner device (clutch mechanism) of the above-described structure, before operation, the clutch plate is supported by the pinion due to the plurality of meshing claws fitting-together with the valley portions of the engaging teeth of the pinion. If some type of external force acts on the clutch plate, there is the possibility that the position of the clutch plate with respect to the pinion will become offset.